1. Field of the Invention
The present invention relates to a cutter fracture detecting system for detecting a fracture of a cutter, and more particularly to a cutter fracture detecting system for detecting a fracture of a cutter which has a plurality of cutting edges.
2. Description of the Related Art
Unmanned operation of a numerically controlled machine tool for a long period of time requires that any fracture of the cutter be detected quickly for a cutter change.
To meet such a requirement, it has been customary to measure the load torque of a spindle, i.e., a drive current of a spindle motor, at all times, generate an alarm when the drive current reaches or exceeds a certain value, stop the machining process, and change the cutter.
However, in the case of a cutter having a plurality of cutting edges such as a milling cutter, the load current of the spindle motor remains substantially unchanged even if one of the cutting edges is broken, and hence it is difficult to detect such a cutter fracture.